Conventionally, there has in some cases been used a so-called a COC (chip on chip) type semiconductor device having a construction of composing a semiconductor circuit of a plurality of chips by interconnecting them one on the other for a purpose of, for example, reducing an occupied area by means of three-dimensioning or standardizing part of the circuit (for example, changing driver circuits based on application by standardizing the memory portions), if the semiconductor device is composed of a plurality of circuits like in the case of a combination of memory portions and the corresponding driver circuits.
As shown, for example, in FIG. 17 showing a process of joining two semiconductor chips 1 and 2, a semiconductor device having the above-mentioned construction is fabricated by fixing the one semiconductor chip 1 on a heated board stage 51 and the other semiconductor chip 2 to a mount head 52, pressing the mount head 52 to permit bump electrodes 11 and 21 made of Au etc. of the respective chips to come in contact with each other under pressure, and heating it to a temperature of 450° C. or so to interconnect these bump electrodes 11 and 21 electrically. Note here that, as mentioned above, the bumps 11 and 21 are made of a metal material such as Au having a higher melting point than solder because the semiconductor device is mounted on the mother board by soldering.
Since the above-mentioned COC type semiconductor device employs high melting point metal such as Au as the material of its bump electrodes, to interconnect a plurality of semiconductor chips thereof, it is necessary to heat them to a temperature of 450° C. or so under pressure in order to obtain good electrical interconnection. When the chips are heated to such a high temperature during interconnection, the semiconductor substrate is also heated to a temperature of 450° C. or higher, so that the circuit elements formed in the semiconductor substrate (elements such as transistors constituting the semiconductor device) are heated to a high temperature, thus fluctuating in properties, which is a problem. Further, although these chips can be joined to each other at a temperature of 450° C. or so, if under pressure as mentioned above, for example, once joined to each other, they cannot be separated without being destroyed in most cases because Au has a high melting point.
In view of the above, it is an object of the present invention to provide such a COC type semiconductor device and a method for manufacturing the same that has a construction which is capable of interconnecting the electrodes of semiconductor chips without being affected by a temperature at which the semiconductor device is mounted and also without deteriorating the properties of the semiconductor chips owing to a high temperature applied thereon.
It is another object of the present invention to provide a semiconductor device having a construction which is capable of securely connecting a bump electrode of a semiconductor chip, even if small, to a partner semiconductor chip.
It is a further object of the present invention to provide a semiconductor device having a construction which is capable of securely connecting each other in the event that one is a wiring.
It is a still further object of the present invention to provide a semiconductor device having a construction which is capable of securely interconnecting a parent chip and a child chip and separating from each other easily without affecting elements in the semiconductor chips when the child chip is removed.
It is an additional object of the present invention to provide a semiconductor chip having such a construction that avoids force from being concentrated on the bump electrode at a joining portion so that the element formed in a semiconductor layer underlying the joining portion may not be affected adversely.
It is another additional object of the present invention to provide a semiconductor manufacturing method which is capable of joining the bump electrodes at a relatively lower temperature and also easily without accurate alignment thereof.